1. Field of the Invention
The present invention relates to a telecommunication system, and more particularly, to a multi-user detection and interference suppression apparatus for femtocell.
2. Description of the Prior Art
In recent years, many novel data communication technologies for the telecommunication system have been developed, such as code division multiple access (CDMA), frequency division multiple access (FDMA), and orthogonal frequency-division multiplexing (OFDM).
CDMA is a channel access method utilized by various radio communication technologies. One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of different frequencies. This concept is called multiplexing. CDMA employs a spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel.
FDMA is a channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, or channels. Multiple access systems coordinate access between multiple users. The users may also share access via different methods such as TDMA, CDMA, or SDMA. These protocols are utilized differently, at different levels of the theoretical OSI model.
OFDM is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
No matter CDMA, FDMA, or OFDM technology is used in the telecommunication system, since multiple user signals from different users are received by the conventional RAKE receiver, a step of multi-user detection is very important and indispensable. However, in practical applications, multi-user detection is notorious for its complexity when it is applied at the basestation (e.g., femtocell). And, interferences occurred among the multiple user signals are so serious that the bit-error-rate (BER) performance and the block-error-rate (BLER) performance of the conventional RAKE receiver become very poor. And, these poor performances of the conventional RAKE receiver should be improved to enhance the communication quality of the telecommunication system.